The study of radio frequency magnetic resonance spectra of samples is facilitated by rotation of the sample about an axis which is usually disposed to coincide with the polarizing magnetic field of the instrument, or at a desired angle thereto. Spinning the sample has the effect of averaging over undesired nonaxial magnetic field gradients. Control of the spin rate is an important function and automated spin rate control in a servo arrangement is not uncommon. Whether a manual or closed loop arrangement, the response time for spin rate control from a faster to a slower rotational rate, is often undesirably lengthy due to the very reduced frictional forces operative in the air bearing. Moreover, the very small variations in the structure of the rotor or stator of the spinner frequently give rise to small rotational torques affecting performance. In the prior art it was known to utilize friction braking, aerodynamic damping (with vanes attached to the rotor), and controlled eddy currents for the purpose of controllably reducing the spinning sets of an NMR sample spinner. These are discussed for example in U.S. Pat. No. 3,911,355.
A typical sample spinner incorporates facility for levitating the rotor within the stator, imparting a rotational torque to the rotor and stabilizing the rotational axis against wobble. These functions are ordinarily accomplished with appropriately disposed pressurized gas jets.